1. Field of Invention
The present invention relates to polymer-based multilayer embedded capacitor devices comprising high dielectric constant polymer-composite thin film material that contains conductive components, and method for producing such multilayer embedded capacitors.
2. Description of Related Art
In electronics, integrating passive components into IC (integrated circuit) packages has the advantages of better electrical performances, higher reliability, smaller sizes, and more design options. Because of the large number of capacitors needed in modern electrical systems, embedded capacitors are of high importance. High dielectric constant polymer thin film is a solution for such embedded capacitors.
Common polymer composite materials for such applications are based on polymer binder combined with high dielectric constant ceramic powder: BaTiO3. The polymer binder materials are usually epoxy or polyimide, which has dielectric constants of 3-6. The polymer composite materials are processed into thin layer of film that is sandwiched between two conductive copper layers. Because of the practical limit of adding high percentage of ceramic powder into the composite material system, the overall polymer composites generally have dielectric constants between 10 to 30, depending on the volume fractions of the ceramic components. U.S. Pat. No. 6,159,611 demonstrated a composite material having a high dielectric constant of 164. That composite material had an extremely high loading of 92% BaTiO3 by weight. With that high loading of inorganic particles, the composite material have low bond strength to copper substrate and are practically difficult to use.
It is much more effective to increase dielectric constant of composite material by using conductive particles than using nonconductive ceramic powders such as BaTiO3. U.S. Pat. No. 6,864,306 used conductive fillers to increase dielectric constant of polymer composite material. U.S. Pat. No. 6,762,237 used conductive carbon nanotube to increase the dielectric constants of polymer composite materials. Percolation theories suggest that the dielectric constant introduce by conductive components is the greatest when the conductive particles concentrations are close to the percolation threshold. The dielectric constants of this type of composite material using conductive additives are reported to be reaching 100 or even 1000.
In addition to the two types of fillers mentioned above: 1) traditional ceramic fillers, such as Barium Titanate, 2) conductive fillers, such as carbon black, carbon nano-tube, and metal particles, there are two new types of material that were recently used to increase dielectric constant of the polymer composite for embedded polymer thin film capacitors: 1) ceramic particles that have conductive domains. 2) coated conductive particles. Ceramic particles with conductive domain was disclosed in U.S. patent application U.S. Pat. No. 12,463,571, coated conductive particles were disclosed in U.S. Pat. No. 6,924,971 and U.S. Pat. No. 7,220,481.
The capacitance of a film is inversely proportional to the thickness of the dielectric film. Therefore, it is desirable to make the embedded capacitor to be thin for achieving high capacitance. Thicknesses of about 8-30 micron has been used in commercial products. The thin thickness creates significant challenges in manufacturing. In Printed Circuit Board (PCB) manufacture processes, large panels of 20 inch or wider are commonly used. It is required that the whole panel to be free of electrical shorting. Even extremely low level of conductive particles or dust can cause shorting across the thickness of the composite film.
The introduction of conductive particles in the thin composite film further increases the risk of shorting. If conductive fillers and or conductive filler aggregates, and/or agglomerate of conductive fillers create connected conductive path across the thickness of the panel, it will cause short-circuit and make the whole panel useless. For highest dielectric constant properties, it is recommended by percolation theory that the conductive particles concentration approaching percolation threshold. At such concentrations, the shorting risks are high. This makes it practically difficult to use. In general, the shorting risks are high when the loading of the conductive components is high, when the size of the filler is big, or when the film thickness is thin, or when the dispersion of conductive particles is poor, or when the conductive particles aggregate. For examples, one single 20 micron diameter aggregate or one 20 micron diameter particle of conductive filler will short the whole 20 inch by 20 inch panel.